An inrush current prevention circuit has been known in which an FET is serially connected to an input line of a switching power supply and a gate voltage of the FET is controlled by a charging voltage of a capacitor to suppress the inrush current when a power supply is connected. See, for example, Japanese Laid-Open Patent Publication No. H9-6440. A current supply circuit supplies a charging current to the capacitor when the power supply is connected. A switching element is connected in parallel to the capacitor. A charging/discharging control circuit turns OFF the switching element when the power supply is connected, to charge the capacitor by a current from the current supply circuit. The charging/discharging control circuit turns ON the switching element when the power supply is disconnected to discharge the charges of the capacitor.
Related techniques are disclosed in, for example, Japanese Laid-Open Patent Publication No. H9-6440.
An AC-DC power circuit converts an AC voltage into a DC voltage to supply a DC power voltage. Immediately after the AC power is supplied, an excessive current may flow due to an inrush current, thereby lowering a voltage of an AC power line which causes an adverse effect.
The present invention has been made in an effort to provide a power device which prevents an inrush current with high reliability and/or high efficiency immediately after an AC power is supplied.